Street Fault from the Salt Lake Oil Field, which underlies much of the Fairfax District north of Hancock Park. The oil reaches the surface and forms pools, becoming asphalt as the lighter fractions of the petroleum biodegrade or evaporate. The asphalt then normally hardens into stubby mounds, which can be seen in several areas of the park.

This seepage has been happening for tens of thousands of years, during which the asphalt sometimes formed a deposit